JPH04295873A - Fixing temperature controller - Google Patents

Abstract

PURPOSE:To offer a fixing temperature controller in which the occurrence of the ripple of temperature is reduced to the utmost regardless of how to use an image forming device. CONSTITUTION:In the case that the consecutive on-time of a heater exceeds the time of Ton even when the temperature of a heat roller does not attain a set temperature, the heater is temporarily turned off, at least, for a Toff time, to wait for the temperature rise by the remaining heat of the heater. Thereafter, whether the temperature of the heat roller attains the set value is judged. When it does not attain the set temperature, the heater is turned on and when it attains the set temperature, the heater is turned off until the temperature thereof becomes under the set value. The ripple of the temperature is restrained to be very small, so that the temperature of the heat roller is kept near the set temperature.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing temperature control device for controlling the temperature of a fixing device installed in an image forming apparatus such as a copying machine or a laser beam printer.

0002

2. Description of the Related Art Image forming apparatuses such as copying machines and laser beam printers are equipped with a fixing device for fixing toner images formed on recording paper. Since this fixing device always needs to be controlled to a certain constant temperature, the temperature is controlled by a fixing temperature control device. The control operation of the conventional fixing temperature control device is as shown in FIGS. 7 and 8. When the power of the image forming device is turned on, the image shown in FIG.
As shown in , the heater is turned on continuously until the surface temperature of the heat roller constituting the fixing device reaches the first set temperature T0 (for example, 150° C.). When the surface temperature reaches the first set temperature T0, the heater is then turned on and off intermittently (for example, repeatedly turned on for 4 seconds and turned off for 2 seconds) until the surface temperature reaches the set temperature Ts. This causes the heat roller to be gradually heated. In this way, when the surface temperature reaches the set temperature Ts, the heater is then turned on and off as shown in the figure to maintain the set temperature, as shown in Figure 8. do. For example, when the set temperature is 170°C, the heater will be turned off when its surface temperature rises above 170°C;
When the temperature drops below 0°C, the heater will be turned on.

0003

[Problems to be Solved by the Invention] However, in the conventional fixing temperature control device that performs such control,
In principle, it is very difficult to maintain the temperature of the heat roller at a constant temperature, and there is a problem in that there is always a temperature ripple within a certain range.

In other words, even if it is recognized that the surface temperature of the heat roller has reached the set temperature Ts and the heater is immediately turned off as shown in FIG.
Due to a delay in response when the heater is turned off, a delay in the transmission of heat from the heater to the surface of the heat roller, and a delay in the response of the thermistor that detects the temperature of the heat roller, the temperature of the heat roller may decrease for a while. A phenomenon occurs in which the value increases. Furthermore, even if it is recognized that the temperature has fallen below the set temperature Ts and the heater is turned on immediately, in addition to the respective response delays described above, the heat capacity of the heat roller and the interference between the heater and the heat roller Due to the heat capacity of the air, the temperature of the heat roller does not rise for a short period of time.

The times at which such a phenomenon occurs can be expressed as an on-time delay time T1 and an off-time delay time T2, respectively. The extent to which the above-mentioned temperature ripple and delay time occur differs depending on how the image forming device is used, but the extent of this ripple becomes large and the temperature of the heat roller becomes considerably higher than the set temperature. When the temperature is too low, paper wrinkles and toner aggregation are likely to occur, and on the other hand, when the temperature is considerably low, the fixing peel strength is reduced.

The present invention has been made in view of the above-mentioned conventional problems, and provides control that predicts the thermal response delay until energization or interruption of the heater causes a change in the surface temperature of the heat roller. An object of the present invention is to provide a fixing temperature control device that can reduce the occurrence of temperature ripples as much as possible regardless of how an image forming device is used.

[0007]

[Means for Solving the Problems] The present invention provides a fixing device for fixing a toner image formed on a recording medium, a heater for heating the fixing device, and a temperature control device for the fixing device. and a temperature control means for controlling energization of the heater based on the temperature detected by the temperature detection means, the temperature control means comprising:
In a thermal fixing device that operates to cut off electricity to the heater when the detected temperature exceeds a set temperature, and to turn on electricity to the heater when the detected temperature is below the set temperature, an on timer that starts counting the continuous energization time at the same time as the energization to the heater starts; an off timer that starts counting the continuous energization time as soon as the energization to the heater is cut off; and an off timer that starts counting the continuous energization time at the same time as the energization to the heater starts; When the time reaches the set time of the on-timer, the power supply to the heater is forcibly cut off, and the continuous off-time of the heater reaches the set time of the off-timer. The apparatus is characterized in that it further includes energization cutoff time control means for outputting a signal to the temperature control means so as to continue cutting off energization to the heater.

[0008]

[Operation] With this configuration, even if the temperature of the fuser has not reached the set temperature, if the continuous on time of the heater exceeds the set time of the on timer, the heater is turned off once for at least the set time of the off timer. wait for the temperature to rise due to residual heat from the heater, then determine whether the fuser temperature has reached the set value, and if it has not, turn on the heater; if it has, turn off the heater until it falls below the set value. It turns out.

Therefore, if the set times of both the off timer and on timer are set to the optimum time taking into consideration the heating or cooling characteristics of the fuser, the temperature of the fuser can be suppressed to a very small temperature ripple and kept close to the set temperature. You will be able to keep it.

0010

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of a laser beam printer equipped with a fixing temperature control device according to the present invention.
FIG. 2 is a perspective view of the fixing device 13 portion shown in FIG.
FIG. 3 is a sectional view taken along line AA in FIG.

As shown in FIG. 1, a photosensitive drum 1 located approximately in the center of this laser beam printer is rotated clockwise in the figure. This photosensitive drum 1
The surface of is first charged to a predetermined potential by charger 2, and then exposed to a laser beam from print head 3 modulated according to an image signal, forming an electrostatic latent image on the surface. Ru. When this electrostatic latent image passes through the developing device 4, a toner image is formed by toner charged with a polarity opposite to that of the latent image, and this is developed.

On the other hand, recording paper, which is a recording medium, is stored in a stack in a paper feed cassette 5 that is detachably provided at the bottom of the main body, and is fed out one by one by a paper feed roller 6, and then transferred to a pair of transport rollers 7 and a timing belt. The image is conveyed via a pair of rollers 8 to a transfer section between a transfer charger 9 and a photosensitive drum 4 . The transfer charger 9 applies a charge having a polarity opposite to that of the toner from the back side of the recording paper, so that the toner image is transferred from the photosensitive drum 1 onto the recording paper. The sheet onto which the toner image has been transferred is further guided by the upper surface of a conveyance guide 10 and conveyed to a nip portion of a fixing device 13 made up of a heat roller 11 and a backup roller 12. As shown in FIG. 3, a heater 21 is provided inside the heat roller 11, and the heater 21 heats the surface of the heat roller 11 to melt and fix the toner on the recording paper. Thereafter, the recording paper is discharged to a face-down tray 16 or a face-up tray 17 on the upper surface of the main body via a pair of transport rollers 14 and a pair of discharge rollers 15. After the transfer, the photosensitive drum 1 continues to rotate clockwise in the figure, and the residual toner on its surface is scraped off by the cleaner 18.
The surface is charged again by the charging charger 2.

Further, as shown in FIGS. 2 and 3, the fixing device 13 is provided with a thermistor 20 as a temperature detecting means for detecting its temperature. This thermistor 20 comes into contact with the surface of the heat roller 11 and detects its surface temperature. Based on this detected surface temperature, the power supply to the heater 21 provided inside the heat roller 11 is controlled as described later.

FIG. 4 is a control circuit diagram of the fixing temperature control device of the present invention. A temperature detection signal from the thermistor 20 that detects the temperature of the heat roller 11 is input to the CPU 30 . The CPU 30, which functions as a temperature control means and an energization cutoff time control means, outputs a control signal for controlling energization of the heater 21 based on this temperature detection signal. Two timers (not shown) are provided inside this. One of the timers is called an on-timer, and the heater 2
Counting is started from the time when energization to 1 is started, and when the count reaches a set value, that is, when the time is up, a signal to forcibly cut off the energization is output. The other timer is called an off timer, which starts counting when the power supply to the heater 21 is cut off, and outputs a signal to permit the power supply when the time is up. Note that the above two timers operate as described above when the temperature detected by the thermistor 20 is lower than the set temperature.

Therefore, when the temperature of the heat roller 11 is below the set temperature, the heater 21 is energized until the on timer times out, and the heater 21 is not energized until the off timer times out. This means that you will not be able to do so. Note that the time set for each of the on-timer and off-timer, that is, the set time, is set to an optimal time that takes into consideration the heating or cooling characteristics of the heat roller 11, but this time may vary depending on the actual machine. Calculated based on the measured values obtained by. Specifically, the setting time of the on-timer is shown in Figure 8.
It is desirable that the setting time of the off timer is approximately equal to the off time delay time T2 shown in FIG.

The temperature detection signal mentioned above is also input to one terminal of the comparator 31. This temperature detection signal is given to the CPU 30 and the comparator 31 as a divided voltage value of the power supply Vcc based on the resistance value exhibited by the thermistor 21 and the resistance value of the resistor R2. Further, to the other terminal of the comparator 31, a divided voltage value of the power supply Vcc based on the resistance values of the resistors R3 and R4 is inputted as a reference signal. The comparator 31 outputs a signal when the magnitude of the input temperature detection signal is larger than this reference signal. The output terminal of the comparator 31 is connected to a power supply Vcc and a logic circuit I through a resistor R5.
The input terminal of C1 is connected. Further, the terminal of the CPU 30 to which the above-mentioned control signal is output is connected to the power supply Vcc and the input terminal of the logic circuit IC1 via a resistor R1. Therefore, the logic circuit IC1 receives the control signal output from the CPU 30 and the signal output from the comparator 31. The signal output from the logic circuit IC1 is inverted by the NOT circuit IC2 and output to the heater control circuit 32. The heater control circuit 32 is NO.
This circuit controls the energization of the heater 21 based on the signal output from the T circuit IC2.

The control circuit having the above configuration operates as follows according to the flowchart shown in FIG. The temperature control process shown in this flowchart is the process performed after the heat roller 11 reaches the set temperature in the diagram shown in FIG. 7, and the heating control until reaching this set temperature is conventional. It is similar to This flowchart will be explained below with reference to FIG. When the temperature control process starts, the CPU 3
0 presets the respective set times of the on timer and off timer provided therein, in other words, the maximum values of the on time and off time, Ton, Toff, and simultaneously sets both timers to 0, and on,
The off flag is reset to 0 (S1). Next, the temperature of the heat roller 11 detected by the thermistor 20 is input, and it is determined whether the temperature is below or above the set temperature (S2). When the temperature is higher than the set temperature, power to the heater 21 is cut off (S3), the count values of the on timer and off timer are set to 0, and the on and off flags are reset (S4 to S6). Then, it is checked whether an error has occurred, such as overheating of the heater 21 or disconnection of the connector, and the process returns to step S2 (S7).
. The above processing is performed after the heat roller 11 reaches the set temperature and when the temperature of the heat roller 11 is equal to or higher than the set temperature.

On the other hand, when the temperature of the heat roller 11 is below the set temperature, it is determined whether or not the on-timer has timed out, and if the time has not expired, the heater 21 is energized (S8, S9). . Then, if the on flag to cause the on timer to count is not set, this flag is set, and if it is set, the on timer is counted (
S10-S12). Further, if the on timer has timed up, the power supply to the heater 21 is cut off (S13
). In other words, as shown in part (A) of FIG. 6, when the temperature of the heat roller 11 is below the set temperature, the energization of the heater 21 is stopped at the time when the on-timer, which is counted up along with the energization, times out. It continues for a certain amount of time. Therefore, even if the temperature of the heat roller 11 has not reached the set temperature as shown in the figure, the heater 21 will not be energized until the time has elapsed. This kind of control is performed because even if heating ends before the temperature reaches the set temperature, the temperature will continue to rise for a while due to the influence of residual heat from the heater 21, and as a result, This is because the temperature will reach close to the set temperature.

After the heater 21 is turned off, if the off flag for causing the off timer to count is not set, this flag is set, and if it is set, it indicates that the off timer has not timed up. Under this condition, the off timer continues counting until the time is up. Furthermore, when the off timer times up, the processes of steps S4 and subsequent steps are performed (S14 to S16). In other words, as shown in part (B) of FIG. 6, when the temperature of the heat roller 11 is below the set temperature immediately after heating the heat roller 11 for a certain period of time, the power supply to the heater 21 is stopped and the power is turned off. Toff when the off timer that counts up times out
It will only be cut off for a period of time. This is heater 2
This is to prevent the heater 21 from being energized while the temperature of the heat roller 11 is rising due to residual heat from the heater 21.

Further, the operation of the fixing temperature control device of the present invention will be explained based on FIG. 6, which shows an example of control. First, after the heat roller 11 is heated to the set temperature, if the temperature falls below the set temperature as shown in part (A) of the figure, if the temperature does not exceed the set temperature during heating, the on-timer Ton time until the time is up,
After the heater 21 is energized, the energization is interrupted. Next, since the temperature detected immediately after this cutoff is below the set temperature as shown in the figure, the energization is cut off for the Toff time until the off timer times up. Note that at this time, the temperature of the heat roller 11 rises due to residual heat from the heater 21. Then, when the off timer times up, the temperature of the heat roller 11 is detected. When the temperature of the heat roller 11 at this time is higher than the set temperature as shown in part (C) of the figure, the current supply is continuously cut off until the temperature falls below the set temperature. Then, when the temperature falls below the set temperature, heating is started again. If the temperature of the heat roller 11 becomes equal to or higher than the set temperature during the heating period, the heating is terminated regardless of whether the on-timer times out.

As described above, control is performed to forcibly cut off the power to the heater 21 or to continue cutting off the power to the heat roller when the on-timer or off-timer times out. This is a case where the temperature No. 11 is below the set temperature. Therefore, if the temperature of the heat roller 11 exceeds the set temperature while the on timer or off timer is counting up, on/off control will be performed with the set temperature as the boundary, as in the past. Become.

In this way, in the present invention, in order to maintain the temperature of the heat roller 11 constant, predictive control is carried out taking into account the heat capacity of the heater 21, and more specifically, the temperature of the heat roller 11 is maintained even after the heater is turned off. Since the control is performed to predict that the temperature of the heat roller 11 will rise to a certain extent due to the heat capacity, and to predict that the temperature will always fall after a certain period of time has passed after the heater is turned off, the above-mentioned method is performed. Since temperature ripples are suppressed, variations in fixing peel strength can be reduced as much as possible. Furthermore, since the temperature does not greatly exceed the set temperature, the occurrence of paper wrinkles and toner aggregation is reduced. Further, although the above embodiments have been described using a laser beam printer as an example, the present invention is not limited to this, and for example, an image is formed by fixing a toner image on a recording paper, as in a copying machine. The present invention can be applied to such image forming apparatuses. Further, although a thermistor has been illustrated as an example of a means for detecting the temperature of the heat roller 11, it may be a thermocouple or the like.

[0023]

As described above, according to the present invention, the temperature of the fixing device can be kept close to the set temperature with extremely small temperature ripples.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a laser beam printer equipped with a fixing temperature control device according to the present invention.

FIG. 2 is a perspective view of the fuser portion shown in FIG. 1;

FIG. 3 is a sectional view taken along line AA in FIG. 2;

FIG. 4 is a control circuit diagram of a fixing temperature control device according to the present invention.

FIG. 5 is a flowchart showing the operation of the control circuit shown in FIG. 4;

FIG. 6 is a diagram showing an example of a change process of the heat roller surface temperature controlled by the control circuit shown in FIG. 4;

FIG. 7 is a diagram illustrating an example of a process of change in the heat roller surface temperature from startup controlled by a conventional fixing temperature control device.

FIG. 8 is a diagram illustrating an example of a change process of the heat roller surface temperature around a set temperature controlled by a conventional fixing temperature control device.

[Explanation of symbols]

11...Heat roller 12...Backup roller 13...Fuser 20...Thermistor (temperature detection means) 21...Heater 30...CPU (temperature control means, on timer, off timer, power cutoff time control means)

Claims (1)

[Claims] 1. A fixing device for fixing a toner image formed on a recording medium, a heater for heating the fixing device, a temperature detection means for detecting the temperature of the fixing device, and a temperature detected by the temperature detection means. and a temperature control means for controlling energization to the heater based on, the temperature control means comprising:
In a thermal fixing device that operates to cut off electricity to the heater when the detected temperature exceeds a set temperature, and to turn on electricity to the heater when the detected temperature is below the set temperature, an on timer that starts counting the continuous energization time at the same time as the energization of the heater starts; an off timer that starts counting the continuous energization time as soon as the energization of the heater is cut off; and an off timer that starts counting the continuous energization time at the same time as the energization of the heater starts When the time reaches the set time of the on-timer, the power supply to the heater is forcibly cut off, and the continuous off-time of the heater reaches the set time of the off-timer. A fixing temperature control device, further comprising a power cutoff time control means for outputting a signal to the temperature control means so as to continue cutting off power to the heater.